Details

Autor(en) / Beteiligte

• Poritz, Mark A.
• Bernstein, Harris D.
• Strub, Katharina
• Zopf, Dieter
• Wilhelm, Heike
• Walter, Peter

Titel

An E. coli Ribonucleoprotein Containing 4.5 S RNA Resembles Mammalian Signal Recognition Particle

Ist Teil von

• Science (American Association for the Advancement of Science), 1990-11, Vol.250 (4984), p.1111-1117

Erscheinungsjahr

1990

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The signal recognition particle (SRP) plays a central role in directing the export of nascent proteins from the cytoplasm of mammalian cells. An SRP-dependent translocation machinery in bacteria has not been demonstrated in previous genetic and biochemical studies. Sequence comparisons, however, have identified (i) a gene in Escherichia coli ( ffh ) whose product is homologous to the 54-kilodalton subunit (SRP54) of SRP, and (ii) an RNA encoded by the ffs gene (4.5 S RNA) that shares a conserved domain with the 7 S L RNA of SRP. An antiserum to Ffh precipitated 4.5 S RNA from E. coli extracts, implying that the two molecules reside in a complex. The 4.5 S RNA can also bind to SRP54 and can replace 7 S L RNA in an enzymatic assay. The product of a dominant mutation in the ffs gene (4.5 S RNA dl1 ) is also coprecipitated by the antiserum to Ffh protein and is lethal when expressed from an inducible promoter. After induction of 4.5 S RNA dl1 , the earliest observed phenotype was a permanent induction of the heat shock response, suggesting that there was an accumulation of aberrant proteins in the cytoplasm. Late after induction, translocation of β-lactamase was impaired; this may be an indirect effect of heat shock, however, because translocation of ribose binding protein or of the porin, OmpA, was unaffected. An unusual separation of the inner and outer membranes, suggestive of a defect in cell envelope, was also observed. Protein synthesis did not cease until very late, an indication that 4.5 S RNA probably does not have a direct role in this process.